1. Field of the Invention
The present invention relates to a motor-driven vertical type injection molding apparatus in which a screw extending in the perpendicular direction is rotationally driven by a measuring motor.
2. Related Background Art
This type of motor-driven vertical type injection molding apparatus has hitherto been constructed such that a molten resin is transferred to a screw tip end portion by rotation of a screw caused by a measuring motor in a measuring step, and a screw back pressure is, however, provided by a servo motor employed as a driving source of an injection mechanism to resist the reactive force (screw back pressure) of the molten resin.
In the prior art described above, during the measurement, vibrations of a servo system are caused by involvement of the molding material between an outer curved surface of the screw and an inner curved surface of a heating barrel for accommodating the screw. The screw back pressure fluctuates on the order of plus or minus several percent. This results in such a problem that it is difficult to give stability to the screw back pressure.